Rhamnolipids are surfactants which can be prepared by means of fermentation. They are composed of one to two rhamnose units and one to three, mostly β-hydroxy fatty acids. The fatty acids can be saturated or unsaturated. The variation in the chain length and amount (congeners) of the fatty acid fractions has been described in a number of publications. (Howe et al., FEBS J. 2006; 273(22):5101-12; Abdel-Mawgoud et al., Appl Microbiol Biotechnol, 86, 2010; pp. 1323-1336). A few covalent derivatives of the fatty acid fractions of rhamnolipids are known. There are primarily a number of rhamnolipid esters described in the literature. Hirayama et al., FEBS Letters, Volume 139, Issue 1, 1982; Pages 81-85, describes the identification of rhamnolipid methyl esters in liquid cultures of Pseudomonas aeruginosa. Miao et al., Journal of Surfactants and Detergents, 17 (6), 2014; 1069-1080, describes the synthesis of di-rhamnolipid ethyl esters by the esterification with ethanol. Miao et al., European Journal of Lipid Science and Technology, 117, 2015; 156-160, describes the preparation of biopolyurethanes from di-rhamnolipid ethyl esters.
WO2001010447 and EP1889623 disclose the pharmaceutical and cosmetic applications of rhamnolipids and short-chain rhamnolipid esters (C1-C6; methyl to hexyl esters, linear or branched), especially for wound healing.
Moreover, Duynstee at al., European Journal of Organic Chemistry, 2, 1998; 303-307 and Bauer et al., Chem. Eur. J. 12, 2006; 7116-7124, describe the chemical synthesis of rhamnolipids; the intermediates synthesized herein are phenacyl esters and benzyl esters of rhamnolipids.